code: def test_union_funcs():
      def a(x):
          pass
  
      def b(x):
          pass
  
      pipelines = [
          compose.FuncTransformer(a) + b,
          compose.FuncTransformer(a) + ("b", b),
          compose.FuncTransformer(a)
          + ("b", compose.FuncTransformer(b)),
          a + compose.FuncTransformer(b),
          ("a", a) + compose.FuncTransformer(b),
          ("a", compose.FuncTransformer(a))
          + compose.FuncTransformer(b),
      ]
  
      for i, pipeline in enumerate(pipelines):
          print(i, str(pipeline))
          assert str(pipeline) == "a + b"
  
file_path: river/river/compose/test_.py
imports: from __future__ import annotations
  import pandas
  from river import compose, linear_model, preprocessing
label_desc: Use image node_id 3 for calling a global function with example usage: test_union_funcs() without return types